What happened:
I used an MCedit filter to change a structure into an (extremely) long command. I then pasted this command into a command block.

What I expected to happen was:
When I would click the button, the structure would appear after a ton of lag.

What actually happened:
The command did not get saved.

After looking into the development console, I found this chunk of error messages:
[21:47:25 INFO]: Client> [21:47:25] [Client thread/ERROR]: Couldn't send command block info
[21:47:25 INFO]: Client> java.lang.IllegalArgumentException: Payload may not be larger than 32k

I think that the new character limit is 32K.